Hydrodynamic delay line



March 11, 1969 w TAYLQR, JR, ET AL 3,432,777

HYDRODYNAMIC DELAY LINE Filed April 29, 1966 4| 5 VENE 9 FLEX 43 37 39 3? GUIDE DELAYED WAVE f 7 ENERGY 7 7 II E VARIABLE ATTENUATOR l5 I7 F J I N (D 2 3 E 2 P J 27 25 WATER g KTR: TANK 29 J PUMP MOTOR 23 DRAIN VALVE John W. Toy|or,Jr.

Gerhard E. Gobl Harold C. Hiscox,

INVENTORS.

BY we A J W .g fl faaovi aa? 1 United States Patent Orifice 3,432,777 Patented Mar. 11, 1969 Claims ABSTRACT OF THE DISCLOSURE A wave guide variable delay line is disclosed. The waveguide is vertical and contains a fluid short the level of which may be varied. Means are provided to couple electromagnetic energy to and from the delay line.

This invention relates generally to a high frequency delay line and more specifically to a variable delay line with wide bandwidth capability, approaching 1 gigacycle, in which a movable liquid short is placed to reflect the incident energy.

In the evaluation of the performance of high resolution radars, there is a need for a variable delay line which can be conveniently varied over a 50 to 100 nanosecond range. These characteristics are far beyond the capabilities of conventional delay devices of the electromagnetic or ultrasonic variety without high levels of dispersion and spurious response.

It is, therefore, an object of this invention to provide a delay line which can be conveniently varied over a 50 to 100 nanosecond range.

Another object of this invention is to provide a delay line of the above specification With wide bandwidth capability.

Further it is an object of this invention to provide a delay line for electromagnetic waves which is extremely accurate and dependable while yet being relatively inexpensive.

This invention together with other objects and advantages thereof will best be understood by reference to the following description and the accompanying drawing in which the single figure is a schematic representation of a hydrodynamic delay line according to the present invention.

Referring now to the figure, a transmission line (waveguide) 5 is shown from which a portion of energy to be delayed is taken by a first electromagnetic coupling means comprising a first directional coupler 7, which has a directivity in excess of 40 db, a fixed attenuator 9 placed at one end of coupler 7, a portion of a flexible guide 11 connected to the other end of coupler 7 and a second directional coupler 13 connected to flexible guide 11. Coupler 13 is connected, thru apertures 15 to a portion of a double ridged wave guide 17 which is approximately 30 feet in length for this particular application. Guide 17 is mounted vertically for receiving a fluid pumped into guide 17 through an opening 19 in the bottom of guide 17. A pump 21 driven by a motor 23 is designed for constant volume over a wide pressure range and is provided for pumping fluid from source 25, through line 27 through pipe line 29 into waveguide 17. Line 29 is also connected to a drain valve 31 for draining fluid from guide 17 thus allowing the fluid level in guide 17 to be varied, which gives a variation of delay obtained by the variation of fluid level in guide 17 thus effectively moving a short which reflects incident energy inside guide 17.

Waveguide 17 is connected to a second electromagnetic coupling means by a second set of apertures 33. Said second electromagnetic coupling means comprising a third directional coupler 35 connected to guide 17, an output waveguide portion 37 connected to coupler 35 containing a variable attenuator 39 which serves as a control for the signal level of the delay wave. Guide 17 is also provided with an attenuator 41, at its upper end, for attenuating any signal not directed through the second set of apertures and a vent 43 which serves as a pressure relief, thereby making it easier to vary fluid level inside guide 17.

The operation is as follows:

Directional coupler 7 is connected to a line 5 containing energy, which it is desired to delay a portion. This energy is fed from coupler 7 thru flexible guide 11, coupler 13, and aperture 15 into waveguide 17. When the energy enters guide 17 it strikes a fluid (preferably water) which reflects it thru the second set of apertures 33 into directional coupler 35. Coupler 35 passes the energy into Waveguide 37, having a variable attenuator 39,- where the energy is selectively attenuated and passed to the source where it is to be used.

A variation of delay is achieved by movement of the short inside guide 17 by changing the fluid height in guide 17, using pump 21-, motor 23 and valve 31.

Using a fluid as the short has the desirable characteristics of conforming to the peculiar shape of ridged waveguide, providing a nonwearing contact, and being easily controllable. Water is an acceptable fluid; conductivity is desired but not mandatory, because the energy is reflected by the discontinuity in dielectric constant.

Using double ridged Waveguide as the transmission line gives the desired minimum dispersion property, and the absence of interior supporting structure makes movement of the short practical.

While the foregoing is a description of 'a preferred embodiment, the following claims are intended to include those modifications and variations that are within the spirit and scope of this invention.

What is claimed is:

1. A hydrodynamic delay line comprising: a vertical Waveguide section; a first electromagnetic coupling means for directively coupling electromagnetic wave energy into said Waveguide section from an electromagnetic source which is to be delayed; a fluid short disposed within said Waveguide section; a second electromagnetic coupling means for directively coupling electromagnetic wave energy reflected from said fluid short; and means for varying the level of said fluid short.

2. A hydrodynamic delay line as set forth in claim 1 further comprising an output waveguide section connected to said second coupling means for receiving said electromagnetic wave energy.

3. A hydrodynamic delay line as set forth in claim 2 wherein said output waveguide section further comprises a variable attenuator for varying the delayed signal level leaving said vertical waveguide section.

4. A hydrodynamic delay line as set forth in claim 1 wherein said first and second electromagnetic coupling means are directional wave guide couplers.

5. A hydrodynamic delay line as set forth in claim 1 wherein said fluid short is a variable level liquid, whereby :he delay of an electromagnetic signal is varied relative to variation of liquid level.

6. A hydrodynamic delay line as set forth in claim 1 wherein said means for varying the level of said fluid short comprises a pump, a liquid storage tank, a valve and fluid communicating means connected between said liquid storage tank and said vertical waveguide section through said ump.

7. A hydrodynamic delay line as set forth in claim 6 wherein said pump is a constant volume pump being driven by a motor whereby the liquid level inside said vertical waveguide section can be varied at a constant rate providing a uniform shorting surface,

8. A hydrodynamic delay line as set forth in claim 1 wherein said vertical Waveguide section comprises a double ridged wave guide section.

4t 9. A hydrodynamic delay line as set forth in claim 1 wherein said vertical waveguide further comprises a vent at the upper portion of said waveguide thereby making it easier to vary fluid level inside said vertical waveguide sections.

References Cited UNITED STATES PATENTS 2,916,615 12/1959 Lundburg 333-31 X 3,005,985 10/1961 Cohn et al.

HERMAN K. SAALBACH, Primary Examiner. PAUL L. GENSLER, Assistant Examiner.

US. Cl. X.R. 

